(Note that the term Roman is to be avoided! It has multiple independent and often conflicting meanings in typography: upright vs italic/oblique, single-byte Latin vs CE/other, or in the style of classical Roman lettering vs not.)

For transliteration, it adds support for International Phonetic Association (IPA), Khmer, Mongolian, another Hindi scheme, pan-Athapaskan native American languages, and the Americanist Phonetic Alphabet (APA). Note that most of the added characters are actually supporting transliteration/phonetic needs.

1 Croatian(Latin) is already supported in AL-3. The digraphs (in practice never user) are included in AL-5.